Optocoupler for the control of high voltage

ABSTRACT

The present invention relates to an optocoupler including a light source having a body and electrical leads, a light detector having a diode stack a metal end cap and electrical leads, and an optical cavity including optically transparent material at least partially covering the body of the light source and the diode stack of the light detector. Also included is a reflective layer including optically reflective material surrounding the optical cavity. The electrical leads of the light source, the metal end cap and the electrical leads of the light detector protrude from the optical cavity and the reflective layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. Divisional Application which claims priorityto U.S. patent application Ser. No. 15/660,008, filed Jul. 26, 2017, thecontents of such application being incorporated by reference herein.

FIELD

The present invention relates to an optocoupler for the control of highvoltage.

BACKGROUND

Performance (e.g. efficiency) of an optocoupler is typically evaluatedbased on current transfer ratio (CTR). CTR is essentially a ratio ofoutput current to input current expressed as a percentage. It is wellknown that as the voltage rating of the optocoupler increases, CTRdecreases. State-of-the-art optocouplers are able to achieve respectableCTRs at low voltages. However, once rated operating voltage reaches acertain level (e.g. above 10 KV), the CTR of these state-of-the-artoptocouplers quickly drops to an unacceptable level (e.g. CTR<0.5%).This is attributed to inefficient optical coupling and packaging ofthese devices.

SUMMARY

An embodiment includes an optocoupler. The optocoupler includes a lightsource having a body and electrical leads, a light detector having adiode stack a metal end cap and electrical leads, and an optical cavityincluding optically transparent material at least partially covering thebody of the light source and the diode stack of the light detector. Alsoincluded is a reflective layer including optically reflective materialsurrounding the optical cavity. The electrical leads of the lightsource, the metal end cap and the electrical leads of the light detectorprotrude from the optical cavity and the reflective layer.

Another embodiment includes a method of manufacturing an optocoupler.The method includes positioning a body of a light source into a firstmold such that electrical leads of the light source protrude from thefirst mold, positioning a diode stack of a light detector into the firstmold such that metal end caps and electrical leads of the light detectorprotrude from the first mold, pouring optically transparent materialinto the first mold to create an optical cavity enclosing the body ofthe light source and the diode stack of the light detector, anddisposing a coating of optically reflective material over the opticalcavity to form a reflective layer.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of an exemplary mass spectrometer utilizing anoptocoupler as a link between a low voltage circuit and a high voltagecircuit, according to an embodiment of the present invention.

FIG. 2 is a block diagram of the mass spectrometer of FIG. 1, showingdetails of an exemplary optocoupler configured with LEDs on a commonside of the optocoupler, according to an embodiment of the presentinvention.

FIG. 3 is a block diagram of the mass spectrometer of FIG. 1, showingdetails of an exemplary optocoupler configured with LEDs on oppositesides of the optocoupler, according to an embodiment of the presentinvention.

FIG. 4 is a representation of a conventional high voltage diode used asa light detector in the output of a high voltage optocoupler.

FIG. 5 is another representation of a conventional high voltage diodeused as a light detector in the output of a high voltage optocoupler.

FIG. 6 is a perspective view illustration of an example of aconventional optocoupler configured with light sources on a common sideoptocoupler directed towards a light detector.

FIG. 7 is a schematic view illustration of the conventional optocouplerin FIG. 6 with light sources impinging on the light detector.

FIG. 8 shows a comparison of axial uniformity between optocouplers witha reflective coating, one without optimized placement of the lightsources (optocoupler 600) and a modified version with optimizedplacement of the light sources, according to an embodiment of thepresent invention.

FIG. 9A shows a perspective view illustration of an exemplary opticalcavity configured with an asymmetric curved surface, according to anembodiment of the present invention.

FIG. 9B shows a side view illustration of the optical cavity in FIG. 9A,according to an embodiment of the present invention.

FIG. 9C shows a bottom view illustration of the optical cavity in FIG.9A, according to an embodiment of the present invention.

FIG. 10A shows a perspective view illustration of an exemplary opticalcavity configured with a symmetric curved surface, according to anembodiment of the present invention.

FIG. 10B shows a side view illustration of the optical cavity in FIG.10A, according to an embodiment of the present invention.

FIG. 10C shows a bottom view illustration of the optocoupler in FIG.10A, according to an embodiment of the present invention.

FIG. 11A shows a perspective view illustration of an exemplaryoptocoupler, according to an embodiment of the present invention.

FIG. 11B shows a schematic view illustration of the optocoupler in FIG.11A, according to an embodiment of the present invention.

FIG. 11C shows the light emitted by the light sources in the optocouplerof FIG. 11A, according to an embodiment of the present invention.

FIG. 11D shows another perspective view illustration of the optocouplerin FIG. 11A, according to an embodiment of the present invention.

FIG. 11E shows a perspective view illustration of the optocoupler inFIG. 11D enclosed in a high voltage cavity.

FIG. 12 shows a perspective view illustration of an exemplary lightsource configured for installation in the optocoupler, according to anembodiment of the present invention.

FIG. 13 shows a perspective view illustration of the exemplary lightsource in FIG. 12, mounted in an optical cavity similar to FIG. 10A,according to an embodiment of the present invention.

FIG. 14 shows a cross sectional view illustration of an exemplarymanufactured optocoupler molded in two layers, according to anembodiment of the present invention.

FIG. 15 is a flowchart of an exemplary optocoupler manufacturingprocess, according to an embodiment of the present invention.

FIG. 16 is a representative graph comparing the CTR to the appliedvoltage across four optocouplers according to embodiment of the presentinvention.

DETAILED DESCRIPTION

Aspects of the present invention provide an optocoupler designed andmanufactured for efficient use in high voltage applications in which theoptocoupler may have several hundred to many thousands of volts acrossits output terminals. The optocoupler is designed and manufactured toincrease optical efficiency when transferring light from a light sourceto a light detector, thereby maintaining an adequate CTR even at higherrated operating voltages (e.g. >10 KV).

High voltage applications are common in various industries. Once suchapplication is in mass spectrometry (i.e. the determination of mass of asample using a mass spectrometer). In general, a mass spectrometer 100(see FIG. 1) typically includes a low-voltage control circuit 102 havingvarious low voltage components (not shown) for controlling the overallmass spectrometer 100 operation. These low voltage components mayinclude memory devices, a processor, etc., as are well known to those ofskill in the art. Also, included are high voltage circuit 106 havingvarious high voltage components (not shown). These high voltagecomponents may include an electron gun, for ionizing the sample undertest, an accelerator plate, for accelerating the ionized sample, amagnet for deflecting the accelerated sample, and a detector fordetecting the deflected sample, again, all of which are well known tothose of skill in the art. The invention is not limited to anyparticular application such as a specific mass spectrometer constructionor to specific low or high voltage components.

For low voltage control circuit 102 to safely control high voltagecircuit 106, without damaging the low voltage components, optocoupler104 is employed as a link between the circuits. Optocoupler 104, throughan optical interaction between a light source (not shown) and a lightdetector (not shown), electrically isolates low voltage control circuit102 from high voltage circuit 106, while allowing control over the highvoltage (e.g. switching electrical currents on/off).

For example, during operation of the mass spectrometer, a processor (notshown) in low voltage control circuit 102, is able to control the highvoltage devices (e.g. electron gun) in high voltage circuit 106, bysending control signals to optocoupler 104. These control signals areconverted by the light source in optocoupler 104 into light beams. Thelight detector in optocoupler 104 then receives these light beams. Uponreceiving the light beams, the light detector modulates the amplitude ofelectrical current flowing through optocoupler 104 to the high voltagecircuit 106 (e.g. the light detector may be configured as a binaryswitch to allow or prevent current from flowing through the high voltagecircuit based upon its detection or non-detection of light, or it mayregulate the amount of current flowing through the high-voltage circuitbased upon the amount of light detected).

One or more light sources and one or more light detectors withinoptocoupler 104 may be arranged in various configurations to performoptical coupling. Two examples of these configurations are shown inFIGS. 2 and 3.

FIG. 2 shows an example for configuring the light sources and lightdetectors of the optocoupler in mass spectrometer 100. In this example,optocoupler 200 includes light emitting diodes (LEDs) 202 and 204 forlight sources, and photo-diodes 206, 208 and 210 for light detection andmodulating electrical current flowing through the high voltage circuit.LEDs 202 and 204 in this example, are positioned on the same side ofoptocoupler 200 and emit light 212 and 214 respectively towardsphoto-diodes 206-210.

FIG. 3 shows another example for configuring the light sources and lightdetectors of the optocoupler in mass spectrometer 100. In this example,LEDs 302 and 304 are positioned on opposite sides of photo-diodes 306,308 and 310. LEDs 302 and 304 in this example, emit light 312 and 314respectively towards photo-diodes 306-310 from opposite sides.

Although FIGS. 2 and 3 show two examples of positioning the LEDs withrespect to the photo-diodes, it should be noted that otherconfigurations are possible (e.g. LEDs and photo-diodes can be placed atvarious positions within the optocoupler to achieve optical coupling).In addition, the optocoupler is not restricted to using two LEDs andthree photo-diodes. Any number of LEDs and any number of photo-diodesmay also be used to produce the optocoupler. In addition, other lightsources (e.g. halogen lamp) and other light detectors (e.g.photo-transistors) may be used.

Typically, the photo-diodes are housed together in a single package.FIG. 4 shows an example construction of such a device 400. The diodes402-412 are connected in series and are typically referred to as a diodestack. The actual number of photo-diodes in the diode stack is based onthe devices voltage rating and the manufacturing process. Metal endcaps414 and 416 are attached to the diode stack ends along with wire leads418 and 420 to make the high voltage electrical connections. The devicemay or may not be encapsulated 422, to protect the structure and providemechanical strength. Although 6 diodes are shown in FIG. 4, it is notedthat any number of diodes could be used to build the stack. In addition,the diodes could have different shapes (e.g. cube, disk, etc.).

For example, FIG. 5 shows another package 500 which includes a stack of3 diodes 502-506 which are shaped as disks. Generally, the shape of thediodes may be chosen based on the overall shape/size of the package, andthe number of diodes in the stack increases as the voltage increases.

The diode stack of FIGS. 4 and 5 is the light sensing component. Theother device components are used to mechanically strengthen the packageand make electrical connections to the diodes in the stack. These otherfeatures do not support incoming light detection.

Once the number, position, and configuration of light sources and lightdetectors is decided, these components are enclosed together in anoptical cavity to create the optocoupler for installation in the enddevice (e.g. mass spectrometer). For example, as shown in FIG. 6,optocoupler 600 includes LEDs 602 and 604 positioned on a common side ofthe optocoupler body. Also included is a photo-diode 606 mountedopposite of and in line with the light emitted from the LEDs 602 and604. Essentially, the body of the photo-diodes and LEDs are enclosed inthe optical cavity, while their electrical leads are positioned toprotrude from the optical cavity. This configuration allows the LEDs tobe electrically connected to the low voltage circuit, and thephoto-diodes to be electrically connected to the high voltage circuit.

Another view of optocoupler 600 is shown in the schematic drawing ofFIG. 7, where LEDs 702 and 704 are positioned on a common side ofphoto-diodes 402/412. These components (e.g. LEDs and photo-diodes) arethen enclosed in an optical cavity 700 which is made from a transparentmaterial allowing optical coupling between the devices.

For example, the components may be positioned relative to each other ina mold which is then filled with a material that is optically clear forthe wavelength of the LED, such as but not limited to, for example,epoxy, plastics, acrylic, glass or silicon. The optical materialprovides a rigid structure for forming the optocoupler body, as well asan optical medium for transferring light between the LEDs andphoto-diodes. This provides a configuration to securely encapsulate thecomponents into a single device that may be used in various applicationssuch as in the mass spectrometer. It should be noted that in thisconfiguration, the electrical leads of the LEDs and the electrical leads(not shown) of the photo-diodes protrude from optical cavity 700allowing for electrical connections to the low voltage and high voltagecircuits respectively.

Positioning of the LEDs relative to the photo-diodes is performed, atleast in part, based on the optocoupler rated operating voltage. Asdiscussed above, operating voltages may be high (e.g. >10 KV) forcertain applications. Higher rated operating voltages require LEDs to bedistanced further from the photo-diodes to prevent the high voltage fromjumping from the high voltage circuit to the low voltage circuit. Thisdistance may be determined based on the optical cavity 700 materialdielectric breakdown strength (i.e. the minimum applied voltage dividedby electrode separation distance that results in breakdown).Specifically, for a given design operating voltage of the optocoupler(such as a maximum design operating voltage, or a maximum designoperating voltage or normal operating voltage multiplied by apredetermined safety factor), the distance is chosen to be greater thanthe distance corresponding to the material's dielectric breakdownstrength.

In addition, positioning of the LEDs relative to the photo-diodes isalso performed, at least in part, based on obtaining a desired opticalefficiency. In general, optical efficiency decreases with an increase indistance between the LEDs and the photo-diodes (e.g. the farther awaythe components are, the less efficient the optocoupler becomes). This isone reason why the optocouplers with a higher operating voltage havelower CTRs. Thus, it is beneficial to set the distance between the LEDsand the photo-diodes to be no larger than necessary (e.g. minimumdistance) to protect the low voltage circuit from the high voltagejumps.

In FIGS. 6 and 7 the optical cavity composes the body of theoptocoupler. Light from the LEDs illuminates everything in the opticalcavity including the diode's active region and other areas of the diodebody that are inactive (metal end caps, electrical leads, etc.) whichleads to lower CTR. This is shown in FIG. 7 where the light emitted fromLEDs 702 and 704 not only impinge on the active region of diodes402-412, but also end caps 414/416 and leads 418/420. In addition, lightthat hits the optical cavity walls is also lost unless the opticalcavity is coated with a reflective material, and then a fraction of thelight is still lost. This lost light reduces the optocoupler efficiency.Optical efficiency is essentially the difference between the lightemitted from the sources and the light received by the detectors.Furthermore, even if the cavity has a reflective layer, the cavity shapealso has an effect on efficiency. For example, cavity 700 in FIG. 7 isrectangular and includes corners. Even if cavity 700 included areflective layer, light beams would become trapped in the corners wherethey reflect back and forth a number of times thereby becoming weaker(i.e. each reflection in the cavity makes the light beam weaker).Optimally, the design should minimize the number of reflections of alight beam before the light beam impinges on the diodes stack.

As can be seen in FIG. 7, light beams emitted by LEDs 702 and 704 becomeincident on the photo-diodes 402-412. However, certain photo-diodes(e.g. 402, 404, 410 and 412), which are directly in front of the LEDs,may receive more light than other diodes (e.g. 406 and 408) that arepositioned indirectly with respect to the LEDs. This is problematic inconventional optocouplers, because very little light, if any, isreflected by the transparent optical cavity towards these indirectlypositioned photo-diodes. This creates what are known as “hot spots”where some photo-diodes (e.g. 402, 404, 410 and 412) receive more lightthan others (e.g. 406 and 408).

Hot spots can be problematic, because the photo-diode's ability toconduct electrical current through the high voltage circuit isproportional to the amount of light impinging on them. Thus, thephoto-diodes (e.g. 402, 404, 410 and 412) that are directly in front ofthe LED may be fully conductive, whereas the photo-diodes (e.g. 406 and408) that are not directly in front of the LEDs receive less light areonly partially conductive.

Problems associated with hot spots may be further exacerbated by thefact that the photo-diodes are electrically connected in series, and thetotal amount of electrical current able to flow through a seriesconnection is limited to the least conductive of the photo-diodes in thestack. For example, if some (e.g. 402, 404, 410 and 412) of thephoto-diodes receives direct light, it may become fully conductivehaving the capability to conduct ‘C’ amps of current. However, if theother photo-diodes (e.g. 406 and 408) are only receiving indirect light,then it may only by half conductive having the capability to conduct C/2amps of current. Due to the series connection between the threephoto-diodes, the maximum current that can flow through the optocouplerwill be C/2 amps, which may be insufficient for the given application.

One solution to this hot spot problem is the use of a reflective layerfor improving what is herein referred to axial uniformity (e.g. theuniformity of light received across all the photo-diodes in the stack).As described above, the LEDs and photo-diodes are molded using a clearmaterial. This provides a medium for light to travel between the LEDsand the photo-diodes. To ensure that all of the photo-diodes (e.g. eventhe diodes indirectly positioned relative to the LEDs) receive a similaramount of light, the optocoupler is coated with a reflective materialhaving a high level of reflectance (e.g. >90%).

For example, the molded optical cavity 700 (once cured) may be insertedinto a second mold which is then filled with a reflective material. Thisreflective material encapsulates the optical cavity and provides asurface that reflects the light beams emitted by the LEDs back to thephoto-diodes. The reflective material may allow both the specularreflection (e.g. light beam is directly reflected in a single direction)and diffuse reflection (e.g. light beam is diffused in many directions)of the light beams.

For example, assume that cavity 700 of the optocoupler in FIG. 7includes a reflective layer (not shown) encapsulating the optical cavity700. The reflective layer reflects light beams emitted from LEDs 702 an704. As the LEDs emit these light beams, the reflective layer reflectsthe light beams one or more times so that the light is uniformlydiffused throughout the optical cavity. Thus, even the photo-diodes thatare indirectly positioned relative to the LEDs receive an adequateamount of light due to these reflections.

As described above, the reflective layer ensures that light beamsattempting to exit the optical cavity are reflected back into theoptical cavity towards those photo-diodes that may not receive directlight from the LEDs. This configuration is beneficial in avoiding the socalled hot spots (e.g. conditions in which some photo-diodes don'treceive enough light).

Shown in FIG. 8 is an optical comparison between received light in acube shaped optocoupler 800 that relies on direct illumination and acube shaped optocoupler 804 that relies on direct and indirectillumination. In both cases, there is a reflective layer around theoptical cavity. More specifically, data plots 802 and 806 show acomparison of light irradiance (e.g. how much light a photo-diodereceives) versus axial position within the optical cavity (e.g. thephoto-diode position relative to the LEDs).

As shown in data plot 802, were the LEDs are oriented directly at thedetector, the irradiance is not uniform. The reflective layer sees asmall portion of the light from the LEDs and scatters it back to thedetector while most of the light from the LEDs directly impinges on thedetector. For example, the photo-diode positioned at axial position 0(e.g. positioned indirectly with respect to the LEDs) receivessignificantly less light than the photo-diodes positioned at axialpositions −2 and 2 (e.g. positioned directly in front of the LEDs). Thisis an indication of hot spots due to non-uniform distribution of light.

In contrast, as shown in the data plot 806, where the LEDs pointindirectly at the light detector, the irradiance becomes more uniform.For example, the photo-diode positioned at axial position 0 (e.g.positioned indirectly with respect to the LEDs) receives almost the sameamount of light as the photo-diodes positioned at axial positions −2 and2 (e.g. positioned directly with respect to the LEDs). This is due tolarger amount of light scattering off the reflective layer.

In many cases, it may not be acceptable to mount the light sources atoblique angles as shown in 804. Instead, the shape of the optical cavityin conjunction with a reflective layer, can improve the optocoupler'soptical efficiency. An example of an optical cavity that accomplishesthis is shown in FIGS. 9A-9C.

In one example, optocoupler 900 is shown in FIG. 9A to have a curvedshape to better reflect the light beams. Specifically, optocoupler 900includes LEDs 906 and 908, cylindrical cavity 904 for inserting ormolding the photo-diode stack (not shown) therein, and a body 902 with acurved upper surface. Although the curved upper surface as depicted inFIG. 9A has an asymmetrical, comma-like geometry, the curved shape mayalso be symmetrical. A side view of optocoupler 900 is shown in FIG. 9B,and a bottom view of optocoupler 900 is shown in FIG. 9C. As illustratedin FIG. 9B, the radius (r) (e.g. 0.06 in.) associated with thephoto-diode stack cavity 904 is smaller than the radius of curvature (R)(e.g. 0.1 in.) of the portion of the optocoupler cavity adjacent thephoto-diodes in the stack positioned furthest from the light sourcesalong a path of travel for incident light from the sources (i.e. thoseto which the light must take the longest path to reach, and which do notlie directly in the path of any light beams emitted from the sources),and the two radii (r) and (R) emanate from different, parallel centeraxes. In the example shown in FIG. 9B, the center axis of the radius (r)for the photo-diode stack cavity and center axis of the radius (R) ofthe optocoupler cavity curved portion define a plane that bisects theoptical cavity into unequal portions. By contrast, in each of theembodiments depicted in, e.g., FIGS. 9B and 10B, the respective axes lieon a plane that bisects the optical cavity into equal portions. In thecomma-shaped geometry depicted in FIG. 9B, the rightmost portion of theoptocoupler cavity curved portion has a radius (R1) that intersects (atpoint T) with a 40 degree line emanating from the base (bottom surface)of the optocoupler shape on one side, and intersects with a curve havinga radius (R2) (e.g. 0.1565 in.), which is larger than (R2) and (r),which defines the leftmost portion of the optocoupler cavity curvedportion, and which connects to the other side of the base. The centeraxes for (R1), (R2) and (r) are parallel to one another (but each pairdefines different planes), the center axis for (R1) intersects withradius (R2), and the center axis for (r) intersects with radius (R1).Although depicted in some of the figures shown to scale with exemplarydimensions, the invention is not necessarily limited to embodimentshaving any specific dimensions. In the embodiments depicted in FIGS. 9B,and 10B, the curved portion of the cavity having the radius (R) (see,e.g., FIG. 10B) intersects with straight lines perpendicular to andemanating from the base. The optocoupler is not limited to anyparticular geometry, as long as a significant amount of the lightproduced by the LEDs either directly or through one reflection uniformlyilluminates the active region of the detector.

In the embodiment depicted in FIG. 10A, optical cavity 1000 geometryincludes the semi-circular cylinder (half-disc) shape mounted atop aright rectangular prismoidal portion. Optical cavity 1000 includes twocavities 1004 and 1006 on the bottom surface for inserting/molding theLEDs therein, and a cylindrical cavity 1002 for inserting/molding thephoto-diode stack. The semi-circular shape along with the placement ofthe LEDs on either side of the photo-diode stack produces a uniformlight distribution along the length of the photo-diode stack.

FIG. 10B shows the distance D2 from the LEDs to the body of thephoto-diode. This distance is determined by the dielectric strength ofthe optical material and maximum operating voltage of the device.

The width of the optical cavity as shown in FIG. 10C is set to be justlong enough to accommodate the active region on the photo-diode. Leavingthe end caps and leads outside of the optical cavity. This improves theefficiency by limiting the light to just the active region of thephoto-diodes (e.g. light is directed to the photodiodes in the stack).

FIGS. 11A and 11D show perspective views of the optical cavity alongwith the photo-diode and LEDs. FIG. 11B shows a schematic view of theassembly highlighting that the optical cavity width is less than thephoto-diode overall length. The assembly shown in FIGS. 11A and 11Bwould then be encased in a diffuse reflective material with similardielectric strength as that of the optical cavity to complete theoptocoupler. For example, optical cavity 1102 is shown to bring the LEDs1108 closer to the photo-diode stack and exclude the metal end caps anddiode leads (e.g. the inactive regions). In this configuration, the bodyof the LED 1108 itself is also minimized in the cavity (e.g. only thelight emitting surface of the LED is located in the optical cavity 1102,thereby decreasing the inactive regions). Essentially, optical cavity1102 partially covers the LEDs and photodiodes such that the activeregions (light receiving diode stack surface and LED light emittingsurface) are enclosed in optical cavity 1102, while inactive regions(electrical leads and end caps) are not enclosed in optical cavity 1102(e.g. they protrude from optical cavity 1102).

Optocoupler 1100 in FIG. 11A includes LEDs, Photodiodes, and has asemi-circular cylinder (half-disc) shape. This half-disc shape may bedesirable because it provides a rounded reflective surface that is moreuniformly radially spaced from the detectors to more uniformly returnlight toward the detectors. This configuration increases opticalefficiency (e.g. light is more uniformly diffused throughout thecavity). Although a rounded shape may be most efficient in some designs,any geometry, including a curved surface that is not rounded orspherical (e.g. parabolic), and including an angled surface or aplurality of polygonal surfaces ranging from a single polygonal face toa collection of polygonal faces that approximates a rounded surface, mayenhance optical efficiency sufficiently relative to a design withoutsuch surfaces by reflecting light along a desired trajectory. Idealgeometries create at least one indirect light path from the light sourceto the optical detector with only a single reflection point.

FIG. 11C shows a model of the light being reflected inside the opticalcavity 1102. In this model, it is shown that the light emitted from LEDs1108 and 1118 impinges directly and indirectly on the active diode stackregion 1114. Indirect light is produced by light beams reflecting fromthe reflective coating on cavity 1102. The number of reflections is alsominimized due in part to the curved geometry (half-disc shape) of thecavity 1102. These factors increase efficiency in the optocoupler whileavoiding hot spots.

In one example, the optical cavities (e.g. 1102) represent volumesformed in a molding process, where the photo-diode stack and LEDs may beinstalled after the mold is cured. In another example, these cavitiesrepresent volumes in the optocoupler where the photo-diode stack andLEDs are molded directly into the optical cavity such that activeregions (light receiving diode stack surfaces and LED light emittingsurfaces) are enclosed in optical cavity 1102, while inactive regions(electrical leads and end caps) are not enclosed in optical cavity 1102(e.g. they protrude from optical cavity 1102).

FIG. 11E shows another perspective view of optocoupler 1100 in FIGS. 11Aand 11D. In FIG. 11E, however, optocoupler 1100 is installed in a highvoltage structure 1130. Structure 1130 protects optocoupler 1100, whileallowing the leads of the diode stack and the LEDs to protrude forelectrical connections to other devices. This configuration may bebeneficial for installing optocoupler 1100 into a larger system.

FIG. 11E also shows features, incorporated into the encasing mold, thatminimize electrical creepage, an important consideration of high voltagecircuitry.

In general, optocoupler 1100 is designed to increase efficiency by oneor more of the following: 1) limiting the overall optical cavity size toonly include the active photo-diode stack regions and the active lightemitting LED surfaces (e.g. electrical leads and end caps are not in theoptical cavity) 2) covering the optical cavity in a coating thatpromotes both reflected and scattered light, 3) using a geometry that isconducive to minimizing a number of reflections required by a beam oflight before impinging on the photodiode stack, and 4) positioning theLEDs with respect to the diodes stack to maximize axial uniformity overthe stack.

The types of LEDs used in these optocouplers may vary in size and shapebased on the LED design, and may include LEDs that emit light in variousspectra (visible spectrum, infrared spectrum, etc.). An example of acompatible LED for installation in the optocouplers (e.g. optical cavity1000 in FIG. 10A) is shown in FIG. 12 as LED 1200. In this example, LED1200 includes a substantially cubic body 1204, a light emitting surface1202, a first external electrical lead 1206, and a second externalelectrical lead (not shown).

The above described LED configuration allows the LED to be inserted ormolded into the optical cavity. An example of the LED inserted or moldedinto optical cavity 1100 is shown in FIG. 13 which depicts a crosssectional view of a portion of the optocoupler 1300 having opticalcavity portion 1304, and LED receptacles 1306 and 1308 where the LEDsare inserted or molded. LED 1200 from FIG. 12 is shown installed in LEDreceptacle 1306 of optocoupler 1300. Note that LED 1200 ismounted/molded into optocoupler 1300 to minimize the amount of LED body1204 (inactive region) that is included in the cavity, therebyincreasing efficiency.

As described above, the optocoupler includes light sources and a lightdetector mounted or molded in an optically clear material at thewavelength of the light sources to form an optical cavity. To improveoptical efficiency, the optical cavity is encapsulated in a reflectivelayer. An example of an optocoupler having these two layers is shown inFIG. 14.

FIG. 14 shows a 2-dimensional side view of a 3-dimensional cube shapedoptocoupler 1400 having an optical cavity 1410, LEDs 1402 and 1404 withleads 1420 and 1422, and photo-diode stack 1406 having leads 1424 and1426 and having multiple photo-diodes 1412, 1414 and 1416 positioned ina stack configuration. Thus, all of the photo-diodes in stack 2006 areevenly spaced along the axis of the stack. In addition, optocoupler 1400has a reflective layer 1408 completely encapsulating optical cavity1410.

Optocoupler 1400 shown in FIG. 14 may be manufactured by a two stagemolding process. This process is described in detail in FIG. 15. Insteps 1502 and 1504 the LEDs 1402/1404 and photo-diode stack 1506 arepositioned within a mold (not shown). The mold may be a threedimensional cast mold that includes mounting positions where the bodiesof the LEDs and photo-diodes can be secured in place within the mold,while allowing their respective electrical leads 1420-1426 to protrudeto the outside of the mold.

In a first molding step 1506, a clear material such as a clear epoxy ispoured into the mold and then oven cured in step 1508. Once the epoxyhas cured, an electrical test is performed on the LEDs and photo-diodesin step 1510. If the LEDs or photo-diodes fail the test, then the deviceis scrapped in step 1512. However, if the LEDs and photo-diodes pass thetest, then a second molding process is performed in step 1514.

Specifically, the cured epoxy extracted from the first mold is insertedinto a second mold which also allows the electrical leads 1420-1426 ofthe LEDs and photo-diodes to protrude from the mold. A reflectivematerial, such as but not limited to a mixture of epoxy and titaniumdioxide is then poured into the second mold to encapsulate the curedclear material (e.g. silicon) and allowed to oven cure in step 1516.Once this second oven-curing procedure is complete, the LEDs andphoto-diodes are once again electrically tested in step 1518. If theLEDs or photo-diodes fail the test, the device is scrapped in step 1520.However, if the LEDs and photo-diodes pass the test, the device isdeemed to be good product in step 1522 and is packaged for sale toconsumers.

In an alternative manufacturing process, the LEDs and photo diodes maybe mounted in the optocoupler after the molding process. For example,the first mold may include a shape that creates cavities forinstallation of the LEDs and photo-diodes. The optocoupler may be moldedwith the clear epoxy, and then the reflective epoxy in a two-stepprocess similar to that described in FIG. 15. However, the LEDs andphoto-diodes may not be inserted into the molds (e.g. the LEDs andphoto-diodes may be mounted into cavities formed during the moldingprocess).

The optocoupler design increases the CTR for a given operating voltageby optimizing the optical efficiency and axial uniformity of the opticalpower. Optical efficiency is the ratio of the optical power hitting thelight detector (i.e. diode-stack) versus the optical power emitted byall the light sources (i.e. LEDs). The axial uniformity of lightreceived by the detectors is computed as(min_intensity/max_intensity)*100), where max_intensity is the maximumintensity of light received by one of the diodes (e.g. diode receivingdirect light) in the stack, and min_intensity is the minimum intensityof light received by one of the diodes (e.g. diode receiving reflectedlight) in the stack. For example, the optocoupler may be designed toachieve an optical efficiency of EFF>50% for a given input of 140 mW ofoptical power, and a uniformity U>85%.

To achieve the desired CTR, the optocoupler design incorporates a numberof design factors. A first factor is the optical cavity volume. Forexample, the design may minimize the optical cavity volume such thatlight has no paths that do not lead to the detector either directly orthrough a single reflection. A second factor is the placement of the LEDwith respect to the detector which maximizes the axial uniformity of thelight hitting the detector by using a combination of direct and indirect(single reflection) lighting. A third factor is ensuring the highreflectance surface is both highly reflective (e.g. preferably >80%reflectivity, or more preferably at least 90%), and causes diffusion sothat it scatters the light in an even pattern. A fourth factor is toexclude or minimize inactive regions (e.g. metal end caps, leads, LEDbody, etc.) from the optical cavity.

In addition, an encapsulant (e.g. epoxy, plastics, silicon, ceramic) maybe used to maintain adequate voltage isolation between the electroniccomponents (e.g. leads). LEDs with an emission spectra wavelength,matched to the peak detector detection wavelength should be used. Theencapsulant can also act as the reflective material and does not need tobe applied in a separate operation.

Although manufacturing includes a second molding process for adding thereflective layer (as shown in FIG. 15), the reflective layer may beapplied to the optical cavity surface by any method known in the art forapplying a coating to a surface, including but not limited spray coatingor other types of mechanical coating techniques, film coating (includingshrink wrapping), vapor deposition processes, chemical orelectrochemical techniques (including powder coating), and the like. Forexample, the cured optical cavity may be coated with a white coating,such as a layer of an acrylic white paint or any coating containingtitanium dioxide or other reflective opacifier or combinations thereof,which acts as the reflective surface. Regardless of the type of coatingstep, it may be desirable to ensure the coating process leaves nouncoated regions or regions that are susceptible to flaking, pin holes,peeling, or other separation of the coating from the optical cavity, asuncoated regions will negatively impact performance. Using a secondmolding process step is ideal for avoiding uncoated spots. Theoptocoupler embodiments described throughout may be implemented invarious high voltage devices. These devices include but are not limitedto a mass spectrometer. In addition, the optocoupler may be controlledto modulate electrical current at various levels through the highvoltage circuit based on the amplitude of the optocoupler input signal,or may be controlled as a binary switch which simply turns the flow ofcurrent ON and OFF through the high voltage circuit.

FIG. 16 is a representative graph comparing the CTR to the appliedvoltage across four optocouplers. Data plots 1602, 1606, and 1608 showthe performance of conventional 6, 10, and 15 KV optocouplersrespectively. 1610 is the trend line rated voltage vs. max CTR for theseoptocouplers. This shows the inverse relationship between Rated Voltageand CTR. Data plot 1604 shows the performance of a 15 KV optocoupleraccording to the present invention. As shown by data plot 1604, theperformance of a 15 KV optocoupler according to a present invention hasmuch higher CTR than data plots 1606 and 1608 showing the performance ofconventional 10 KV and 15 KV optocouplers.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather various modifications may be madein the details within the scope and range of equivalence of the claimsand without departing from the invention.

The invention claimed is:
 1. A method of manufacturing an optocouplercomprising: positioning a body of a light source into a first mold suchthat electrical leads of the light source protrude from the first mold;positioning a diode stack of a light detector into the first mold suchthat metal end caps and electrical leads of the light detector protrudefrom the first mold; pouring optically transparent material into thefirst mold to create an optical cavity enclosing the body of the lightsource and the diode stack of the light detector; and disposing acoating of optically reflective material over the optical cavity to forma reflective layer.
 2. The method of claim 1, wherein the step ofdisposing the coating of optically reflective material over the opticalcavity further comprises the steps of: placing the optical cavity into asecond mold such that the electrical leads of the light source and themetal end caps and electrical leads of the light detector protrude fromthe second mold; pouring the optically reflective material into thesecond mold to create the reflective layer, wherein the reflective layerfully covers the optical cavity; and extracting the optocoupler from thesecond mold.
 3. The method of claim 1, further comprising: positioningthe body of the light source and the diode stack of the light detector adistance away from each other in the optical cavity before pouring theoptically transparent material into the first mold, the distanceselected to be greater than a distance corresponding to a dielectricbreakdown strength of the optically transparent material at a designoperating voltage of the optocoupler.
 4. The method of claim 1, whereinthe light detector comprises a plurality of photo-diodes, the methodfurther comprising: providing the diode stack about an axis thatintersects the optical cavity before pouring the optically transparentmaterial into the first mold.
 5. The method of claim 1, furthercomprising: selecting a shape for the optical cavity that achieves apredetermined uniformity and a predetermined efficiency of lightreceived by the light detector.
 6. The method of claim 1, furthercomprising: minimizing a volume of the first mold by spacing the lightsource and the light detector based on a design operating voltage of theoptocoupler, dielectric breakdown strength of the optically transparentmaterial, and uniformity of light received by the light detector.